Fruit maturity varies between vineyards,
between vines in the vineyard, between
clusters on a vine, and between berries on
a cluster.

is the source
of considerable variation in vintage
quality, which, in turn, forms one of
the bases for the existence of an entire
“industry” of wine judges, consumer
magazines, and related services.

The majority of the fluctuations in
fruit composition are caused by climate
variability. In fact, weather differences
among years, in addition to vineyard
location, are by far the strongest determinants
of fruit composition.9 Such climatic
differences often trump seasonal
differences in soil moisture (except at
the far low and high ends of the moisture
spectrum) in both dry-farmed and
irrigated vineyards.19,25,34

The Science of Grapevines is a
new 400-page book that comprehensively
explores the physiology of
the grapevine as it occurs around the
world. It focuses on the whole plant
rather than at the cellular and organ
levels, providing an understanding of
whole-plant function. Comprehensive
coverage of the role of water relations
and temperature prepares the
reader for changing climate impacts.
Worldwide information on grapes
and grape-related industries provides
important insights into implications
of differences – and similarities.

The truly unique approach of this
book is the scientifically-grounded
exploration, often applying discoveries
in other plant species, of the
main physiological processes underlying
grapevine form and function,
their interactions, developmental
and environmental control, and
their implications for practical vineyard
management.

Uniform fruit composition is often
described as a critical factor for premium
wine making and is equally
desirable for the production of grape
juice, table grapes, and raisins. It could
be argued, however, that less uniform
fruit may sometimes result in
more complex wine, and this might be
one of the rationales behind blending
wines from different vineyard sources.
In many European wine regions, such
blending was traditionally done in
the field, where a range of clones
or even cultivars were interplanted,
sometimes systematically and sometimes
randomly.

crunchiness
or crispyness, and visual appearance,
including color,24 although
Muscat flavor is often also sought after.
Seedlessness is important in some table
grape markets and is usually desirable
for raisin grapes, for which high sugar
content is much more important than
it is for table grapes.

Fruit composition changes over time
during the berry ripening period as
part of the grapevine’s developmental
program and is therefore under
genetic control. In addition, like phenology
and yield formation, the extent
of these changes may also be modulated
by environmental factors and by
the interaction of these factors with the
genotype of the vine. It is often difficult
to separate the influence of one of
these factors from that of another.

For example, solar radiation affects
both incident light and tissue temperature.
An increase in water supply
leads to an increase in shoot growth,
which can decrease the proportion of
exposed leaves, which, in turn, alters
both light quantity and light quality,
and may also lead to changes in
canopy microclimate (Chapter 5.2).
Furthermore, the sugar concentration
is higher and the malate concentration
lower in berries that have
fewer seeds, apparently because veraison
occurs earlier in such berries.7,28
Thus, even within a grape cluster,
there is often a natural variation of
sugar concentration in the range of
5° to 7° Brix that results from asynchronous
development of individual
berries.6 Due to such asynchronous
development, neither time nor thermal
time after bloom adequately reflects
the developmental stage and maturity
of individual berries in a sample from
the entire population of berries on a
vine, let alone in a vineyard.

Any factor that influences vine
growth and metabolism directly or
indirectly impacts fruit composition,
and this leads to large variation
among growing seasons in terms of
fruit quality. Wine grape production
is especially sensitive to climate variability.
This sensitivity

Markus Keller is the Chateau Ste. Michelle Distinguished Professor of Viticulture at
Washington State University’s (WSU) Irrigated Agriculture Research and Extension
Center in Prosser, WA. He received his master’s degree in agronomy (plant science)
in 1989 and a doctorate in natural sciences in 1995 from the Swiss Federal Institute
of Technology in Zürich. He has taught and conducted research in viticulture and
grapevine physiology on three continents, including Swiss Federal Research Station for
Fruit-Growing, Viticulture and Horticulture in Wädenswil (now Agro-scope Changins-
Wädenswil); Cornell University in Geneva, NY; and Charles Sturt University (Wagga
Wagga, Australia), before joining WSU in 2001.THE SCIENCE OF GRAPEVINES: Anatomy and Physiology(ISBN
#9780123748812) was published February 2010 by Academic Press, Elsevier (elsevierdirect.com).